Method and device for making intricately-shaped axisymmetric parts from hardly deformable polyphase alloys

ABSTRACT

A method for making an intricately-shaped axisymmetric part having a central portion and a peripheral portion, comprises simultaneously rotating a blank structure fixed on a shaft and forming a peripheral portion of the blank using a forming tool having at least three degrees of freedom (i) at a temperature above 0.4 the blank melting point but below the temperature of secondary recrystallization, (ii) at a rate of from 10 −3  to 10 2  s −1 , and (iii) for a rotation period to effect stress relief in the portion being formed. A device for making intricately-shaped axisymmetric part having a central portion and a peripheral portion, comprising an axial blank structure fixing and rotating unit including a fixture for interchangeably installing a mandrel including a built-up mandrel; at least one roll with a carrier; actuating mechanism for rotating and displacing the roll relative to a blank structure fixed by the unit; a furnace for heating the blank structure fixed by the unit, the furnace having a movable portion disposed around a window for introducing the roll into the furnace; wherein the movable portion of the furnace is axially movable together with the roll over an entire working stroke length of the roll.

BACKGROUND OF THE INVENTION

[0001] The invention relates to plastic metal working, more specificallyto a method for producing a precision blank for parts such asintricately-shaped disks that feature considerable variations inthickness and diameter and deep non-forgeable undercuttings.Particularly, the invention relates to producing an intricately-shapedaxisymmetric part from a blank of hardly deformable polyphase alloy,particularly from a heat-resistant nickel alloy.

[0002] “GatorizingTM” is a method for making a part from a hardlydeformable alloy by die-forging of a fine-grained blank undersuperplasticity conditions. At a first stage of the method, asuperplastic intermediate product is produced by intense plasticdeformation (deep-drawing extrusion), and the at a second stage of themethod, the product is subjected to die-forging. The method can producean axisymmetric part of a relatively intricate shape, e.g.,small-diameter bladed disks. However, the capabilities of said method ismuch restricted due to a disadvantage inherent in the die-forgingtechnique and consisting in that virtually each part is made in its owndie set. Thus, the greater the number of parts to be produced, thegreater number of expensive die sets is required. In addition, themethod requires use of powerful press-forging equipment and expensivesturdy forging dies.

[0003] A more versatile and less power-consuming rolling method forproducing an intricate part, comprises local forming by rolling a blankhaving a central and a peripheral portion. In this method, anintricately shaped part is attained by using a polyphase alloy blankmade from a structure prepared for superplastic deformation. Localforming of the blank is effected under controlled thermomechanicalconditions at temperatures within a range exceeding 0.4 the meltingpoint but below the temperature of secondary recrystallization of theblank material, and at deformation rates of from 10⁻³ to 10² s⁻¹. Thecentral blank portion is deformed by compression or by compression andtorsion, using tools appearing as quills, while a peripheral portion isdeformed by rolls having at least three degrees of freedom and operatingwith a specific force:

σ_(s)>q≧σ_(τ)  (1)

[0004] where σ_(τ) is the flow stress of the blank material in thedeformation zone of the peripheral blank portion; σ_(s) is thedeformation resistance of the blank material in the deformed zones ofthe blank central and peripheral portions and q is the pressure(specific force) exerted by the tool on the blank.

[0005] Die-forging cannot be used directly to produce a disk part havinga variable cross section. Forging such a part requires forming ahot-type projection composition at the stages preliminary to theforging. The local forming method enables making an axisymmetric partthat is too complicated constructionally to be made by the die-forgingtechnique. A distinguishing feature of the local forming method is adeformation condition that establishes favorable distribution ofstress-and-deformation states over the blank. When forming intricatelyshaped parts, the value of deforming loads must be very specific toavoid deformation of an already formed thin-walled blank portion,inasmuch as the thin wall blank portion is liable to deform even at lowstress values, especially when in a state of superplasticity. In ageneralized aspect, favorable distribution of a stressed state in ablank is represented by relationship (1).

[0006] However, there are axisymmetric parts that have a central portionand a peripheral portion, wherein the peripheral portion not only has anintricate profile and a well developed surface, but also a volume andsurface area that substantially exceed the volume and surface area ofthe central portion. In addition, a narrow shape of the peripheralportion may be non-forgeable or undercuttings may prevent forging.Forming such an intricately shaped peripheral portion of a blankinvolves rolling of with large degrees of deformation. However, this isattainable only under hot deformation conditions, includingsuperplasticity conditions. Despite the fact that under such conditionsflow stress of the material is rather low, deformation (displacement) ofa sturdy peripheral blank portion requires heavy loads, i.e., forces andspecific forces, which are even larger at the so-called “rigid end” ofthe blank As a matter of fact, such rigid end in the rolling procedureunder consideration is the zone of constrained (hindered) deformationcharacterized by a distance between an outside and an inside diameter ofsaid rigid end. During the rolling process the rolls exert pressure onthe rim inner surface, but in order that the blank diameter increase,the deformation center should be developed to the rim external surface.The longer said distance, the greater pressure (specific force) must beexerted on the blank. The size of the blank rigid end can be evaluatedby the ratio between the above said diameters. When said ratio exceeds1.5 to 1.8, it is necessary to apply such pressure and force that willchange the size and shape of the already formed thinner disk portion(web) as well. The ratio between the axial dimensions of the central andperipheral portions (i.e., the disk rim being rolled and the disk webhaving been rolled) is limited to approximately the same value. Hencethe volume and weight of peripheral disk portion being rolled are alsorestricted on the whole.

[0007] Web deformation preventing techniques fail to solve the problemof rolling a blank having a robust. Thus, web resistance must beincreased for a local forming method by hardening the material byintercooling. However, the degree of practicable intercooling isrestricted to the thermal conductivity factor of the material and thedanger of overcooling the portion being deformed to criticaltemperatures at which plasticity of the alloy is badly affected and theflow stress increases which in turn leads again to an increase indeforming forces. Otherwise, uncontrolled cooling will result in grainsize variations. The radial deformation rate may not be reducedsubstantially as well, since in this case the tool-to-blank contactpattern is decreased and hence the deformation center is decreased, too,which to a greater extent will add to the influence of the rigid end.One of the conditions for carrying into effect local forming process,according to the prototype, is the provision in the blank of a structureprepared for superplastic deformation. Preparation of a fine-grainedstructure is carried out according to a separate rather labor-consumingtechnological process concerned with a necessity for carrying out anintense blank deformation.

[0008] Thus there is a need for a local forming method to produceintricately-shaped large-size axisymmetric parts from hard-to-deformpolyphase alloys to make precision parts having an intricately shapedwell developed peripheral portion.

BRIEF DESCRIPTION OF THE INVENTION

[0009] The present invention provides a local forming method for theproduction of intricately-shaped large-size axisymmetric parts fromhard-to-deform polyphase alloys. According to the invention, a methodfor making an intricately-shaped axisymmetric part having a centralportion and a peripheral portion, comprises simultaneously rotating ablank structure fixed on a shaft and forming a peripheral portion of theblank using a forming tool having at least three degrees of freedom (i)at a temperature above 0.4 the blank melting point but below thetemperature of secondary recrystallization, (ii) at a rate of from 10⁻³to 10² s⁻¹, and (iii) for a rotation period to effect stress relief inthe portion being formed.

[0010] Also the invention provides a device for makingintricately-shaped axisymmetric part having a central portion and aperipheral portion, comprising an axial blank structure fixing androtating unit including a fixture for interchangeably installing amandrel including a built-up mandrel; at least one roll with a carrier;actuating mechanism for rotating and displacing the roll relative to ablank structure fixed by the unit; a furnace for heating the blankstructure fixed by the unit, the furnace having a movable portiondisposed around a window for introducing the roll into the furnace;wherein the movable portion of the furnace is axially movable togetherwith the roll over an entire working stroke length of the roll.

[0011] In an embodiment of the invention, a method for making a parthaving a central portion and a peripheral portion, comprisespreconditioning a blank structure for superplastic deformation; formingthe blank structure into the shape of a sleeve having a monotonicallynarrowing shape in a first step, forming a complete peripheral portionof the sleeve in a single second step (i) at a temperature above 0.4 theblank melting point but below the temperature of secondaryrecrystallization, (ii) at a rate of from 10⁻³ to 10² s⁻¹, and (iii) fora rotation period to effect stress relief in the portion being formed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 represents the diagram of a device adapted for carrying theproposed method;

[0013] FIGS. 2-11 represent type of parts which can be produced by theproposed method;

[0014]FIG. 12 illustrates the photographs of parts the types presentedin FIGS. 3, 7, and 9;

[0015]FIG. 13 illustrates photographs of the part, which is presented inFIG. 11;

[0016]FIG. 14 illustrates a photograph showing the instant of completinga technological process for production of a part;

[0017]FIG. 15 illustrates a photograph showing the working zone properduring the process for producing a part (the furnace top being out ofposition);

[0018]FIG. 16 represents the diagram of performing essentially firstoperation of forming a sleeve-type part using a single roll and aforming mandrel.

[0019] An original shape of the blank peripheral portion and an initialroll position are indicated with a dotted line;

[0020]FIG. 17 illustrates a diagram of a final forming operation of asleeve-type part having a monotonically varying shape using a singleroll.

[0021]FIG. 18 illustrates a diagram of forming a sleeve-type part havinga monotonically varying taper shape using a single roll and a formingmandrel.

[0022]FIG. 19 illustrates a sketch of a part following the formingprocedure using a built-up forming mandrel;

[0023]FIG. 20 illustrates a diagram of a forming procedure of a flangein the peripheral portion of a sleeve-type part having a monotonicallyvarying shape using a single roll and a built-up forming mandrel.

[0024]FIG. 21 illustrates a diagram of a forming procedure of parthaving the peripheral portion bilateral relative to the central portionthereof and having a monotonically varying shape using a single roll andbuilt-up forming mandrels.

[0025]FIG. 22 illustrates a diagram of a forming procedure of asleeve-type part having a monotonically varying shape using an externalforming mandrel and a single roll; and

[0026]FIG. 23 illustrates a diagram of a forming procedure of asleeve-type part having a monotonically varying shape using rollersdisposed on opposite sides of the peripheral blank portion.

DETAILED DESCRIPTION OF THE INVENTION

[0027] In this specification, the recitation of one element, feature orstep shall mean one or more of the element, feature or step. A “blank”is an unfinished metal or alloy such as a billet. The term “titanium”includes titanium metal, alloy, composite and other titanium-containingcompositions. The term “aluminum” includes aluminum metal, alloy,composite and other aluminum-containing compositions. A “quill” is ahollow shaft. A process of “stress relief” is a low temperatureannealing process to reduce residual stress in a blank that may resultfrom work hardening or quenching. The term “generatrix direction” meansa direction toward the center of a blank structure away from aperipheral portion.

[0028] The present invention has for its object to provide a method formaking, from polyphase alloys, intricately-shaped axisymmetric partshaving a central portion and a well-developed peripheral portion, and toensure high production output of the forming process.

[0029] In addition, one more object of the invention is to extendprocessing capacities due to the use of blanks having a fine- andcoarse-grained structure and of the deformation conditions correspondingto the blank structure.

[0030] The aforesaid object is accomplished in a method for makingintricately-shaped axisymmetric parts from hardly deformable polyphasealloys, said parts having a central portion and a peripheral portion,which method consisting in that an appropriately shaped blank having astructure prepared for superplastic deformation, is set fixably androtatably in a quill and that the blank peripheral portion is subjectedto local forming at temperatures exceeding 0.4 the melting point butbelow the temperature of secondary recrystallization, at a rate of from10⁻³ to 10² s⁻¹, using a local forming tool having at least three ordersof freedom, CHARACTERIZED in that use is made also of a blank having astructure not prepared for superplastic deformation, wherein at leastpart of the already shaped peripheral blank portion, irrespective of thestructure thereof, has the outside diameter exceeding the diameter ofthe finished part, or the inside diameter less than the diameter of thefinished part, and local forming is performed using at least a singleroll by reducing the blank peripheral portion in the direction of thegeneratrix thereof, and the period of blank rotation relative to thelocal forming tool is preset to be not less than the time of intenserelaxation of stresses in the areas being deformed; used as quills atthe first step for at least the blanks having a coarse-grainedstructure, is a forming mandrel having a diameter corresponding to theinside or outside diameter of the peripheral portion of the shaped blankor of the finished part.

[0031] Some of the aspects or embodiments of the invention include:

[0032] rotating an aluminum alloy blank structure relative to a formingtool for a period of rotation not in excess of 0.25 s;

[0033] rotating a titanium alloy and heat-resistant nickel alloy blankstructure relative to a forming tool for a period of rotation between0.25 and 100 s;

[0034] rotating a coarse-grained blank structure relative to a formingtool for a period of rotation between 50 and 100 s;

[0035] rotating a fine-grained blank structure relative to a formingtool for a period of rotation between 10 and 50 s;

[0036] rotating a submicrocrystalline blank structure relative to aforming tool for a period of rotation between 0.25 and 10 s;

[0037] forming in a number of steps depending on profiling and structureof a blank;

[0038] single step forming of a sleeve-shaped blank structure preparedfor superplastic;

[0039] two step forming of a central portion and peripheral shapedportion shaped blank structure prepared for superplastic steps, whereina sleeve-shaped blank is formed in a first step;

[0040] forming a coarse-grained original blank structure having acentral portion and a thin-walled peripheral projection,, whereinforming is performed by first preparing a sleeve-shaped blank and thenby subjecting the peripheral portion to 50-75% reduction undertemperature and deformation rate conditions of superplasticity;

[0041] forming an original blank by performing several steps of reversalroll motion;

[0042] local forming of a peripheral portion of a blank with a formingmandrel is used to produce a part having wide variations of thicknessand diameter in adjacent sections;

[0043] a forming mandrel is used to form an interior surface;

[0044] a forming mandrel is used to form an exterior surface;

[0045] a built-up forming mandrel is used;

[0046] maintaining mandrel forming surface temperature within a range ofsuperplasticity of the blank material;

[0047] local forming of the peripheral portion using a single roll toproduce a sleeve-type part having a monotonously narrowing profile,

[0048] local forming of the peripheral portion using a single roll and aforming mandrel having an outside diameter equal to a minimum insidediameter of the peripheral portion to produce a sleeve-type part havinga monotonously narrowing profile,

[0049] two rolls disposed on opposite sides of a wall being formed forlocal forming of the peripheral portion is carried out using;

[0050] two rolls disposed on opposite sides of the wall being formed,and a forming mandrel, wherein one roll and the mandrel are used in afirst step, and both rolls are used in a second step; and

[0051] heating temperature of the surface being deformed of theperipheral portion of the part within a range of from the deformationtemperature to a temperature exceeding the lower temperature thresholdof superplasticity for performing a fine-grained heat-resistant nickelalloy;

[0052] Carrying the herein-proposed method into effect is possible in adevice comprising units that provide for axially fixing the blank andits rotation, at least one roll with its carrier, a working furnace withopenings in the walls for part of the fixing unit and the roll to bringinto the furnace, and actuating mechanisms for the roll to rotate anddisplace. In addition the furnace walls have a movable portion disposedaround the opening for bringing the roll into the furnace, said devicebeing characterized in that the blank fixing unit is provided withfixtures for installing change mandrels, built-up ones inclusive, andthe movable portion of the working furnace wall is axially movable,together with the roll, over the entire length of the preset rollworking stroke.

[0053] The method can also be carried into effect provided that:

[0054] the blank fixing unit has a shaft and sleeves for impartingtorque to the blank;

[0055] the roll carrier further comprises a heat shield.

[0056] A combination of features of the proposed invention provides forsolving its problem due to the provision of a favorable distribution ofthe stressed-strained states in the blank, with which states, as hasbeen pointed out before, the stresses in the zone of deformation arehigh enough for plastic flow of material in the direction predeterminedby the tool, while in other zones the stresses are below the levelinitiating plastic deformation. In this case, the favorablestressed-strained states are understood to mean not only correspondenceof deformation values to the shape assumed but also forming or retaininga required deformation structure, in particular, without accumulatingflaws dangerous to the forming process or operating conditions, andwhenever possible, provision of homogeneity of said structure.

[0057] Now let us assess the effect of the geometric factors, i.e., thedimensions of the blank volume being displaced and the deformation rate,on the relationship (1) which represents, in a generalized aspect, afavorable distribution of the stressed-strained states.

[0058] An average pressure value q exerted by the roll on the blank isdefined as

q=F/S,   (2)

[0059] where S is the area of the tool-to-blank contact pattern; and Fis a complete force exerted by the tool on the blank on the contactpattern area.

[0060] The value of said force can also be expressed by virtue ofinternal stresses in the body being deformed

F=n_(σ)σ_(i)S,   (3)

[0061] where n_(σ) is the stressed state factor, which depends on thesize of rigid blank end and σ_(i) is the intensity of internal stresses.

[0062] With a sufficient correctness for an engineering analysis one mayassume that deformation at a preset rate in the peripheral blank portionbeing deformed occurs whenever the stress intensity σ_(i) reaches acertain flow stress value σ_(τ), said value depending on the deformationrate ξ.

σ_(τ)=Kξ^(m)   (4)

[0063] where K is an empirically determined coefficient; and m is theflow stress rate response.

[0064] Having used expressions (2), (3), and (4), we obtain thefollowing equality:

q=nKξ^(m)   (5)

[0065] In the precedent equations ξ denotes an average deformation rateof each local area per blank revolution (i.e., the period of blankrotation relative to the roll). Instantaneous value of the deformationrate of each local area may be defined as follows:

ξ_(m) =V/L,   (6)

[0066] where V is the velocity of metal crowding onto the tool; and L isthe length of blank-to-tool contact in the direction of metal crowding.

[0067] With a constant amount of reduction by the tool (in a directiontowards the axis in the proposed method, and between the rolls in theprototype), V consists of two components. viz., V_(τ)—blank peripheralvelocity and V_(a)—axial rate of tool displacement (which is the radialrate V_(τ) for the prototype). In the scalar representation the equationof linear velocities may be written as V_(τ) ²=V+V_(a) ²)^(1/2). Takingthe latter in consideration we obtain:

ξ_(m) =V/L=(V _(τ) ² +V _(a) ²)^(1/2) /L   (7)

[0068] An average velocity per blank revolution equals

ξ=ξ_(m) Δt/T,   (8)

[0069] where Δt is the residence time of a local area (contact pattern)under the tool; and T is the blank rotation period.

[0070] In its turn, T=Δt+τ, where τ is the time of idle run of the areabeing deformed; since τ>>Δt, it may be assumed that T≅τ, wherebyξ≈ξ_(m)Δt.

[0071] The parameters used are associated with one another as follows:Δt=L/V_(r); V_(r)=ωR; ω=2π/T, where ω is angular velocity, R is thecurrent deformation radius of the peripheral blank portion, π≈3.14.

[0072] Hence the instantaneous and average velocities may be representedrespectively as follows:

ξ_(m) =V _(r) /L×[1+(V _(a) /V _(τ))²]^(1/2) ≈Δt ⁻¹×[1+(V _(a) /V_(τ))²]^(1/2)   (9)

ξ=τ⁻¹×[1+(V _(a) /V _(τ))²]^(1/2)   (10)

[0073] and substituted expression (10) to expression (5) we obtain:

q≅K×n _(σ)×τ^(−m)×[1+(V _(a) /V _(τ))²]^(m/2)   (11)

[0074] or else, when taking into account that V_(τ)=ωR and ω=2π/T theexpression (11) may appear in another aspect:

q≅K×n _(σ)×τ^(−m)×[1+(V _(a)τ/2πR)²]^(m/2)   (12)

[0075] Expression (12) holds true both for the proposed method and theprototype, but in the latter case velocity V_(r). is to be substitutedin expression (12) instead of V_(a).

[0076] In expression (12) the value enclosed in square bracketsapproximates unity, since in forming large-size parts the circumference(2πR) exceeds substantially the tool feed rate per revolution ((V_(a)τ)and hence the relation (V_(a)τ/2πR)² is a small value.

[0077] Having simplified expression (12), we obtain:

q≅K×n_(σ)×σ^(−m)   (13).

[0078] Thus, equation (13) common to both the herein-proposed method andthe prototype demonstrates that when leaving out of account thecoefficients K and m representing the effect of the structure which isquite admissible in case of hot deformation under the ÑÏÄ conditions,while the pressure depends on the period of τ . . . Insofar as τ islocated in the denominator so with its rise q decreases, and withreduction of q the value of τ increases. However, a change in the period□ influences but dissimilarly the value of q in the proposed method andin the prototype, this being due to the coefficient n_(σ). Thus,reduction of said period in the proposed method leads to an inverselyproportional increase in the value of q, because the rigid blank enddoes not influence in this case the value of q and the coefficient n_(σ)which is practically a constant number approximating unity.

[0079] In the prototype the pressure depends on the size of the blankrigid end and the deformation center. The coefficient n_(□) depends onsaid parameters nonlinearly. As the deformation rate increases thevalues of the stresses effective in the region being deformed increase,too. As a result, intensity σ₁ of said stresses is changed so that inorder that said intensity reaches again a higher value of the flowstress σ_(τ) corresponding to a higher deformation rate, it is necessaryto further increase the tool pressure.

[0080] Therefore when the deformation rate increases, the pressure risesnot only due to an increase in the flow stress resultant from saiddeformation rate but also due to the effect produced by the blank rigidend. It is said effect that the coefficient n_(σ) represents whichranges within 2 and 5. Hence the same specific tool force applied to theblank corresponding to the condition of the expression (1), in theproposed method provides for higher level of flow stress σ_(τ) in theblank peripheral portion and accordingly a higher deformation rate andoutput of the process as compared to the prototype.

[0081] Thus, absence of a mutual effect of the period and the stressedstate factor enables one to substantially enhance the effect of stressincrease due to a reduced period of blank rotation, according to theproposed method provided that the condition of expression (1) isobserved.

[0082] Besides, according to the proposed method, the output may beincreased not only due to a reduced period of blank rotation but alsodue to a change in the ratio between velocities V_(A)/V_(τ), whichcannot be done, as has been pointed out before, in the prototype, sincewhen V_(er) is decreased the effect of the stressed state is increased,and when V_(t) is increased, there is augmented, as will hereinafter bedemonstrated, the moment of force resulting in deformation of thealready formed blank portion.

[0083] Selection of the period of blank rotation is concerned with somespecific features of deformation during local forming of the blankperipheral portion.

[0084] The nature of deformation in the proposed technical solution issuch that each area of the blank peripheral portion being deformed ismany times subjected to a cyclic action of the tool due to the fact thatthe blank rotates relative to the tool and the latter performstranslation motion towards the generatrix of the blank peripheralportion. During direct tool exertion on the blank within the local siteof deformation, shear stresses are therein effective which displace theblank material in the direction predetermined by the tool. Once anyblank area has come out of contact with tool, and during the tool idlerun till a next tool contact with the blank relaxation of the blankmaterial occurs so that the stresses caused by the tool are reduced. Atthe microstructure level density of defects is reducing during saidrelaxation of the material, which is due to, e.g., annihilation ofdislocations. Insofar as the deformation center exceeds the zone ofdirect blank-to-tool contact on the area of the tool action, especiallyfor a fine-grain structure, i.e., the extent of the deformation centerin the direction towards said generatrix is perceptibly larger than therate of tool feed per blank revolution, part of the blank material issubjected repeatedly by the tool action during blank rotation relativeto the tool. When the blank rotates for a period of time not in excessof the time of intense relaxation, stress values are reduced severaltimes so that defects that change substantially the structural state andmechanical characteristics of the blank material, in particular, shearstress and plasticity have no time to accumulate therein. A number ofspecially performed experiments are the evidence of the fact. In saidexperiments there were determined the time of intense relaxation of flowstresses after releasing the test specimen from the load during tensiletest. The experiment also included comparing the levels of plasticityand flow stresses of test specimens subjected to continuous andintermittent (cyclic) tension. In this case, intermittent tensile testinvolved releasing the test specimen from load for a period of restexceeding the time of intense relaxation of stresses. It was establishedthat stresses in a high heat-resistant alloy dropped several times for atime lapse of the order of 1 to 5 seconds. In addition, the stress levelin a test specimen cyclically deformed with a predetermined period wasapproximately the same as in the test specimen subjected to continuousdeformation, and percentage elongation was 1.5 to 2 times higher.

[0085] In the prototype, when a period of blank rotation relative to thetool is reduced, the tangential force component F_(□) constituting amoment is increased. Said moment together with the radial forcecomponent F_(r) acts in the same rolling plane, thus twisting andtensioning, respectively, the web in its minimum cross-section. Tosubstantially reduce the component F_(r) is impossible, since thedeformation center should be well developed. Therefore with a reducedperiod the sum of forces acting on the deformed blank portion isincreased.

[0086] According to the proposed method, an increase in F_(□) due to afast-rate hardening tells but insignificantly on the rise of stresses inthe blank formed portion, since said force is less than in theprototype, inasmuch as the contact area in the respective direction issmaller. The other component, i.e., the axial force F_(a) also fallsshort of being rather large and may therefore be preset within arequired value using two ways of which the first one involves anappropriate selection of the value of q in accordance with theabove-considered relationships, while the other procedure is based onvarying the value of S, forasmuch as the method can be carried outeither at a single step (in case of a higher value of S) or at a numberof steps (with a lower value of S), since in this case there is noeffect of the blank rigid end (1).

[0087] Thus, the feature consisting in that blank rotation period is notin excess of the time of intense relaxation of the blank deformedportions is one of the principal and adequate features for providingfavorable deformed state of the blank material allowing deformation ofsaid material with high degrees of deformation without accumulation ofdefects, and one of the features indispensable for accomplishing theobject of the invention.

[0088] To attain higher output and adhere to the relationship (1), i.e.,to provide favorable stressed-strained state, it is reasonable to reducethe blank rotation period until it is equal to the relaxation time anddecrease the axial tool displacement speed for the period of blankrotation, i.e., the tool rate of feed per blank revolution. Linearvelocity of tool displacement is in this case determined by the productof the number of blank revolutions per minute by the rate of tool feedper blank revolution. In addition, reduction of the axial tooldisplacement speed will result in reduction of the respective forceacting as a tensile force with respect to the formed zone of the blankperipheral portions, that is, conditions for obeying the relationship(1).

[0089] Use of quills as a forming mandrel, according to the proposedmethod, improves stressed-strained state at least when the peripheralportion of coarse-grained blanks is deformed, said portion featuringflow stress exceeding that in said portion of fine-grained blanks. Thisis also promoted by friction forces acting in the opposite directionrelative to the aforementioned forces, tending to change the shape andsize of the deformed blank peripheral portion.

[0090] Finally, it is worth noting that forming the blank peripheralportion in the direction towards its generatrix is in fact neither asingle nor unambiguous way of local forming parts having well developedperipheral portion. Such parts may be made according to anotherproduction process technique and from a blank shaped differently than inthe proposed method. In particular, such parts may be manufactured froma blank having its peripheral portion shaped in the plane of the centralportion thereof which can then be “laid” onto the mandrel using rotaryreduction technique. However, such a method fails to solve the problem.Moreover, all disadvantages inherent in the prototype will interferewith it during the preforming process the blank peripheral portion withthe aid of, e.g., rolling the blank to the required dimensions.

[0091] In the subordinate claims the relaxation time depends on a numberof factors, such as temperature, nature of the alloy used, and itsstructure. Thus, the higher the temperature of superplastic deformationand the lower the grains size, the faster proceeds the stress relaxationprocess. For instance, a longer relaxation period is required forheat-resistant alloys in case of deformation at a temperaturecorresponding to the lower superplastic deformation range, whereas forusual fine-grained alloys deformable at high superplastic deformationtemperature a shorter period (5 s)is required, for titanium alloys, 5 s,and for aluminum alloys, 0.25 s.

[0092] Relatively short periods of repeated action in forming the blankperipheral portion are especially favorable for local deformation offine-grained structure blanks, since relaxation processes proceedrapidly in such structure and the latter provides for high technologicalplasticity of the blank material. The influence exerted by the nature ofan alloy on the period of blank rotation and the relaxation time isambiguous; thus, for instance, the relaxation time in polyphase nickel-or titanium-base heat-resistant alloys is longer than in, e.g., aluminumalloys. However, the former alloys have lower thermal conductivity ascompared to the latter one, so that a deformation-induced localtemperature rise may expedite relaxation, though the heat releasedshould not be causative of an inadmissible overheating. Experimentalchecking has evidenced that the rotation period in forming titanium-baseand heat-resistant blanks should not be in excess of 100 s.

[0093] Further additional essential features also develop and definemore exactly possibilities of accomplishing the object of the presentinvention.

[0094] According to the proposed method, the blank peripheral portion isformed with the aid of a forming mandrel.

[0095] The presence of friction between the blank and the mandrel on adeveloped contact surface, according to the proposed method, as distinctfrom the prototype, makes possible, with lower contact stresses(hold-down pressure), providing blank rotation during local forming.Moreover, according to the proposed method, only one out of threevectors of deformation forces acts, as a moment of force, on the blankcentral portion. However, stresses resulting from said moment are butinsignificant, since as distinct from the prototype, they are reduced byrather high value of a high polar moment of resistance of the centralcross-section.

[0096] When making parts having their peripheral zone shaped as a sleevetapering with respect to the web, the peripheral bank portion issubjected to forming in two steps; first a straight sleeve is formed,having a diameter not less than the diameter of the bottom, then byreduction on a sectional forming mandrel or without such a mandrel, bydrawing the walls until the finished size is obtained.

[0097] Local forming is effected at a several steps the number of whichis determined depending on the degree of the blank preforming and on theblank structure, which is concerned with that an original blank can beobtained by the various metallurgical techniques, such as casting,die-forging, powder metallurgy, or a combination thereof.

[0098] In particular, when a possibility is provided for use of a blankpreformed as a sleeve and having a structure prepared for superplasticdeformation, the number of operations of local forming may bepractically as little as one.

[0099] At the same time, the method is also realizable if use is made ofa blank having its structure prepared for superplastic deformation andpreformed as a central portion and a peripheral projection.

[0100] Furthermore, to use a blank preformed in the way mentioned aboveis expedient if said blank has an original coarse-grained structure.Herein an indispensable prerequisite is the provision of a thick-walledprojection which ensures, during subsequent deformation, conversion of amicrostructure of the blank into a micro- or submicrocrystalline.

[0101] Regardless of the final profile of the part it is recommendedthat at the first step of the local forming process the blank be shapedas a sleeve, using a forming mandrel. In some cases said shape may bethe final one of the part to be obtained.

[0102] Whenever it is necessary to obtain a part having an extendedthin-walled peripheral portion, it is recommended that the formingprocess be performed at a number of steps which provides for optimumconditions for applying the deforming load. It is due to varying thepathway of the tool (i.e., roll), changing it he angle of incline to theblank rotation axis, as well as the roll penetration depth that one caneffect control over the degree of deformation within a wide range ateach step, thereby providing the most favorable conditions for deformingthe blank peripheral portion. This is of paramount importance when ablank is used, wherein a coarse-grained structure is established in theoriginal state of the peripheral portion thereof. As it is commonknowledge [3], a coarse-grained structure is characterized by a muchrestricted resource of technological plasticity in case of hotdeformation which might result in disturbing the continuity of the blankmaterial in attempting to make axisymmetric parts having awell-developed thin-walled peripheral portion from hardly deformablematerials. Therefore when using a blank whose peripheral portion has acoarse-grained structure, it is necessary that at the initial steps saidstructure be transformed into a microcrystalline one with a particlesize of 1 to 10 □m or into a submicrocrystalline structure with aparticle size less than 1 □m so as to prepare a structure amenable tosuperplastic deformation.

[0103] A proper selection of the specific values of the degrees ofdeformation and the temperature-and-rate conditions for at least part ofthe steps required for preparing the blank structure for superplasticdeformation depends on a number of factors, viz., chemical and phasecomposition of the alloys used, final shape of the part peripheralportion, requirements imposed on the structure and mechanicalcharacteristics of the finished part. The degree andtemperature-and-rate conditions of deformation are selected to beadequate for dynamic recrystallization to occur in the blank material,in the course of which a microcrystalline structure is established. Itis worth noting that a microcrystalline structure may be established inthe blank peripheral portion at a number of steps. At a first step apartially recrystallized structure is established, then at a second step(which may be the final) a completely recrystallized structure isestablished in the blank peripheral portion. Such a technique makespossible substantially reducing the value of specific forces, as well aspromoting more complete stress relaxation, which is especially importantfor polyphase alloys. In particular, for instance, as far asdispersion-solidifying nickel alloys are concerned, at a first step itis necessary to eliminate the hardening effect of a second phase due toits coagulation, disturbing coherent association with the matrix and itspartial dissolution. An insignificant degree of deformation at the firststep expedites substantially the processes of coagulation of the secondphase, and selection of maximum values of the period of blank rotationprovides for more favorable conditions for stress relaxation due toprocesses of dynamic polygonization and recrystallization leading toformation of a partially recrystallized structure.

[0104] Moreover, use of a number of steps make possible step-to-steptemperature reduction which contributes to further refining ofmicrostructure of the blank peripheral portion down to a submicron grainsize. Provision of a submicrocrystalline structure in the blankperipheral portion makes it possible to substantially shorten the stressrelaxation period, thereby enhancing the output of the process involved.

[0105] Process capabilities of the proposed method can be extended dueto a technique, wherein the forming process is effected revering theroll motion.

[0106] In this case repeated deformation is carried out by analogy withbackward extrusion, thus enhancing the output of the process.

[0107] One of the recommended conditions of making a part withconsiderable variations in thickness and diameter in adjacent sectionsis performing local forming of the blank peripheral portion using aforming mandrel. This facilitates meeting the conditions of relationship(1), which eventually adds to the production accuracy of a part as togeometry and dimensions.

[0108] Constructionally, a forming mandrel may be either solid orbuilt-up, which can be made use of depending on the shape of the blankperipheral portion. Whenever the blank peripheral portion has adecreasing outside diameter and terminates with a flange, i.e., when theforming mandrel fails to be withdrawn from the interior space of thepart after the forming process, use is to be made of a built-up formingmandrel.

[0109] The mandrel may be either external or internal depending on theshape of the external and internal surface thereof.

[0110] As a rule, mandrels are made of a more heat-resistant materialthan that of a blank to be worked, e.g., from a cast high nickel alloy.To provide adequate construction strength of the mandrel the latter isto be more robust than the blank. Inasmuch as the mandrel is inpermanent contact with the blank being deformed, an intense heattransfer occurs, especially in cases where local intercooling of themandrel is used through the unit of fixing the blank central portion tothe mandrel. In such a case it is recommendable to effect a strictcontrol over the mandrel heating temperature so that the temperature ofthe mandrel forming surfaces corresponds to a temperature range ofsuperplasticity of the blank material.

[0111] When making thin-walled parts such as a sleeve with monotonicallyvarying shape, local forming of the blank peripheral portion ispracticable using a single roll, or a single roll and a forming mandrel.In some cases the mandrel may be constructionally shaped in such amanner as not to follow the internal shape of the blank peripheralportion, but has such a size that are sufficient to fix the blank inposition and retain the already formed cantilevered blank portion sandprevent it from distortion. That is why the mandrel has an outsidediameter equal to a minimum inside diameter of the blank peripheralportion.

[0112] When manufacturing large-diameter parts having a well-developedperipheral portion, it is recommended that local forming of the blankperipheral portion be performed using two rolls disposed on oppositesides of the wall being formed, or be made at a preceding step using aroll and a forming mandrel.

[0113] It is expedient that making parts having a bilateral blankperipheral portion, relative to the central blank portion, be effectedby local forming the blank peripheral portion with two rolls at a time,said rolls moving in opposite directions from the blank central portion.Using such a technique is instrumental in substantially increasing theoutput of the process, or alternatively, local forming of the blankperipheral portion may be performed consecutively with a single rollusing reversal of the roll motion. Choosing between said two techniquesdepends both on economic advantage of their use and on the shape of thepart obtained.

[0114] When forming blanks from heat-resistant alloys, resort may bemade, with a view to increasing tool endurance and mandrel rigidity, tointercooling of both. However, a difference may occur between thetemperature of the blank heated up to the deformation temperature andthe less heated roll and mandrel. Therefore it is necessary in suchcases to maintain the temperature of heating the surface of theperipheral portion being deformed within the range from the deformationtemperature to a temperature exceeding the temperature threshold ofsuperplasticity for a fine-grained material. Otherwise with a presetdeformation rate the overcooled surface layers will be deformed undernon-optimum superplasticity conditions. Hence strain hardening of thesurface layers of the blank peripheral portion will result from localforming. On performing final heat treatment of such parts with a view toenlarging, by one or two orders of magnitude, the grain size, zonalgrain size variations are liable to occur which impairs badly mechanicalcharacteristics of the finished part.

[0115] When a blank is deformed, especially a nickel alloy blank, uponstress relaxation, even occurring under most favorable conditions, someresidual stresses are likely to remain which are concerned with a changein the blank geometry but produce no influence on the forming process ofa part but may result in zonal grain size variations developing uponsubsequent high-temperature heating. For completely eliminating residualstresses and ruling out any possibility for developing grain sizevariations following the process of forming parts from nickel alloys, itis recommendable to preheat blanks from the alloy ageing temperature toa temperature below that of complete dissolution of the strengtheningphase, followed by holding at that temperature for 1 to 24 hours.

[0116] To obtain parts with a maximum accuracy and shape and sizestability, it is also recommendable to combine the last step of thefinal forming of the blank peripheral portion with calibration which isconducted at a deformation temperature and involves penetration of rollsinto the blank for a depth not exceeding the size tolerance value forthe finished part.

[0117] The proposed method can be realized in a device whosedistinguishing feature consists in that the fixing unit is provided withpositioners of change mandrels, the built-up ones inclusive, and themovable portion of the working furnace is axially displaceable togetherwith the roll throughout the length of the preset roll working stroke.

[0118] In the known technical solution the fixing unit appearing as twoquills is adapted for fixing the blank central portion in position andimparting torque and its replacement involves dismantling the entiredevice. In the proposed device all the above listed functions of thefixing unit are retained and, in addition, whenever necessary said unitis imparted the functions of a tool. The construction arrangement of thefurnace provides for local forming of the blank peripheral portion inthe direction towards its generatrix.

[0119] Thus, construction arrangement of the proposed device enables oneto manufacture intricately shaped parts having a well-developedperipheral portion.

[0120] The operating capabilities of the device can be further extendeddue to the following additional features.

[0121] When the working furnace is additionally provided with a separatechamber adapted for accommodating the tool, while inoperative, andpreheating it, the production cycle will thereby cut down substantially.Besides, since the roll weight is cardinally less than the weight of themandrel and blank before the local forming procedure, so the roll isexpedient to be preheated to a temperature lower than that in theworking furnace.

[0122] A construction arrangement wherein communication between saidchamber and the interior space of the working furnace is establishedthrough an opening in the movable portion of the furnace wall rendersthe device more space saving.

[0123] In cases where the roll is introduced into the furnace togetherwith its carrier it is expedient that the roll-to-carrier attachmentunit be provided with ducts for the refrigerant to supply and withdraw,as well as that the roll carrier be provided with a heat shield.

[0124] When making parts having a central hole and an extendedperipheral portion, use is made of shaft provided with sleeves forhigher rigidity, said sleeves serving also for torque transmittingpurpose.

[0125] When effecting local forming with two rolls disposed on oppositesides of the blank peripheral portion, it is suggested that use be madeof rolls adapted to move radially and axially in step with each otherand to mutually turn through an angle of from zero to π/2.

[0126] Features of the invention will become apparent from the drawingsand following detailed discussion, which by way of example withoutlimitation describe preferred embodiments of the invention.

[0127]FIG. 1 represents the diagram of a device adapted for carrying theproposed method. FIGS. 2-11 represent type of parts which can beproduced by the proposed method, FIG. 12 illustrates the photographs ofparts the types of are presented in FIGS. 3, 7, and 9. FIG. 13illustrates photographs of the part the type of which is presented inFIG. 11. FIG. 14 illustrates a photograph showing the instant ofcompleting a technological process for production of a part (the furnacetop being out of position). FIG. 15 illustrates a photograph showing theworking zone proper during the process for producing a part (the furnacetop being out of position). FIG. 16 represents the diagram of performingessentially first operation of forming a sleeve-type part using a singleroll and a forming mandrel. An original shape of the blank peripheralportion and an initial roll position are indicated with a dotted line.FIG. 17 illustrates a diagram of a final forming operation of asleeve-type part having a monotonically varying shape using a singleroll. An initial roll position is indicated with a dotted line. FIG. 18illustrates a diagram of forming a sleeve-type part having amonotonically varying taper shape using a single roll and a formingmandrel. An initial roll position is indicated with a dotted line. FIG.19 illustrates a sketch of a part following the forming procedure usinga built-up forming mandrel. FIG. 20 illustrates a diagram of a formingprocedure of a flange in the peripheral portion of a sleeve-type parthaving a monotonically varying shape using a single roll and a built-upforming mandrel. An initial roll position is indicated with a dottedline. FIG. 21 illustrates a diagram of a forming procedure of parthaving the peripheral portion bilateral relative to the central portionthereof and having a monotonically varying shape using a single roll andbuilt-up forming mandrels. An initial roll position is indicated with adotted line. FIG. 22 illustrates a diagram of a forming procedure of asleeve-type part having a monotonically varying shape using an externalforming mandrel and a single roll. FIG. 23 illustrates a diagram of aforming procedure of a sleeve-type part having a monotonically varyingshape using rollers disposed on opposite sides of the peripheral blankportion. Ref. No. 5 in FIGS. 16-23 denotes a blank, Ref. No. 11 denotesa roll, Ref. No. 19 denotes a solid forming mandrel, and Ref. Nos. 20,21, and 22 denote the component of a built-up forming mandrel. Curvedarrows in FIGS. 16-22 indicate the senses of rotation of the blank androlls.

[0128] The following Examples are illustrative and should not beconstrued as a limitation on the scope of the claims unless a limitationis specifically recited.

[0129] The device (FIG. 1) for carrying the herein-proposed method intoeffect comprises fixing units 1 and 2 which are coaxially arranged andare provided with drives (not shown in FIG. 1) for being displaced withrespect to each other along ways 3 and 4 provided on a bed (not shown inFIG. 1) and for imparting rotation to a blank 5, reversible rotationinclusive. The fixing units are interconnected through a shaft 6provided with sleeves 7 through which torque is transmitted to the blank5. The bedway 9 mounts a carriage 8 provided with a drive of its own(not shown in FIG. 1) for its being displaced along a bedway 9, i.e.,lengthwise the axis of the blank rotation. The carriage 8 mounts a rollcarrier 10 with a roll 11. Drives for the roll to displace are not shownin FIG. 1. Indicated at Ref. No. 12 is a high-temperature furnace forheating the blank and maintaining a preset temperature thereof duringthe deformation procedure. The furnace is provided with a movableshutter 13 having an opening 14 for the roll to introduce. The furnacealso has windows 15 and 16 for the components of the fixing units 1 and2 to pass through. The roll carrier 10 is equipped with a heat shield17. The device is further provided with a separate chamber 18 adapted toaccommodate the tool, while inoperative, and for preheating.

[0130] For forming the blank 5 shown in FIG. 1 the device furthercomprises forming mandrels 19 and 20.

[0131] The following Examples are illustrative and should not beconstrued as a limitation on the scope of the claims unless a limitationis specifically recited.

EXAMPLE 1

[0132] A sleeve-type part was to be produced with its peripheral portionhaving a bilateral shape tapered in a direction away from the blankcentral portion, said part being made of the titanium alloyBT25(Ti-6.5Al-4Zr-2Mo-1.5Sn-1W). Local forming was performed using apreformed blank having a central portion and a peripheral portion shapedas bilateral projection. The blank having an outside diameter of 450 mmand thickness of the projections equal to 25 mm and 30 mm, respectivelywas prepared by the die-forging procedure, whereby a 5-micronhomogeneous globular microcrystalline structure of the microduplex typewas established. Used as the original blank for die-forging was acylindrical blank cut from a 390-mm diameter casting The blank having acast structure was subjected to a multistep deformation involving a90-degree turn of the direction of deformation in a diphase region in a1600-ton press under quasi-isothermal conditions. As a result of suchworking a microcrystalline structure was established in an upset washerwhich structure was then deformed using an isothermal die-forging blockat 950□. Preparatory to local forming the forged piece was subjected torough machining in order to remove the oxidized metal layer and making acentering hole.

[0133] A forming diagram of a sleeve-type part with its peripheralportion having a bilateral shape tapered in a direction away from theblank central portion, made of the BT25 titanium alloy is presented inFIG. 3.

[0134] Local forming of the blank was carried out in a device whoseschematic diagram is represented in FIG. 1. The blank together with theforming mandrels was secured in the fixing unit, whereupon the furnacewas closed and heated to a deformation temperature (950° C.). At thesame time rotation was imparted to the blank through the sleeves set onthe shaft of the blank fixing unit so as to ensure a uniform blankheating. A first step of local forming of the blank peripheral portionwas carried out using the forming mandrels and a single roll, both beingmade of the alloy grade AEÑ6Ó(Ni-9Cr-9.7W-5.5Al-2.6Ti-1.6Mo-1.1V). Theheating temperature of the blank and mandrels in the working furnace was950° C. The roll was heated in the preheating chamber to a temperatureby 100 to 200° C. below that stated hereinafter. The roll was broughtinto the working furnace together with its carrier through the windowprovided in furnace movable wall. The roll-to-carrier attachment unitwas subjected to intercooling beforehand with compressed air passedthrough the ducts made in the roll carrier. Local forming procedure waseffected at a number of steps using a single roll and a mandrel. Theperiod of blank rotation with respect to the roll was 25 s.

[0135] At a first step one of the projections was locally formed intothe shape of the type of cylindrical sleeve. At the first pass thethickness of the first projection was reduced from 25 mm to 15 mm. In asimilar way there was performed the local forming of the otherprojection whose thickness was reduced to 12 mm for two passes usingreversal of the roll motion. In this case another mandrel was used,since the inside diameter of the second projection was somewhat smallerthan that of the first one.

[0136] Thereupon the cylindrical mandrels were replaced with thebuilt-up ones corresponding to the internal shape of the blankperipheral portion, and local forming of the walls of sleeves formed atthe first step was carried out using two tools, that is, built-upmandrels and a roll, under the above stated temperature-and-rateconditions. First final forming of the first projection was performed,then the second projection was formed using the same roll.

[0137] A photograph of the finished part is shown in FIG. 12. As can beseen from said Figure, just after the final forming procedure the parthas a homogeneous fine-grained macrostructure over the entirecross-section thereof.

EXAMPLE 2

[0138] A sleeve-type part was to be obtained from a blank made of theBT25 titanium alloy, with its peripheral portion having a bilateralshape tapered in a direction away from its central portion, the blankand the deformation conditions being the same as in Example 1.

[0139] The local forming procedure was effected as follows.

[0140] Use was made of two rolls and two forming mandrels. At a firststep the projections were subjected to local forming into the shape ofthe type of cylindrical sleeve accompanied by penetrating the rolls intothe blank material and their displacement in the opposite directionsaway from the blank central portion. At a second step the projectionswere subjected to final local forming with two rolls at a time, usingbuilt-up forming mandrels.

[0141] The result was the finished part similar as to shape andstructure to that of Example 1.

EXAMPLE 3

[0142] A sleeve-type part was to be obtained from a blank made of theBT25 titanium alloy, having its peripheral portion unilaterally taperedin the direction away from the central portion thereof. Local formingwas effected using a preformed blank having a central portion and aperipheral portion shaped as a unilateral projection. The blank havingan outside diameter of 450 mm and a 25-mm thickness of the projectionwas prepared by a die-forging procedure, whereby a 5-micron homogeneousglobular microcrystalline structure of the microduplex type wasestablished. The structure preparing procedure and the final formingconditions were similar to those of Example 1.

[0143] A forming diagram of a sleeve-type part having its peripheralportion unilaterally tapered in the direction away from the centralportion thereof, from the BT25 titanium alloy is presented in FIG. 7.

[0144] The local forming procedure was effected as follows. At a firststep the forming was carried out using one roll and one forming mandrel,at the second step use was made of only a single roll.

[0145] The final step of the local forming procedure was combined withcalibration. In this case the disk peripheral portion is rolled over itsprofile at specific forces effective in the contact patter causingplastic deformation of the blank the value of which was not in excess ofthe tolerance limits specified in the drawing. Performing such anoperation made it possible to stabilize the size and shape of a finishedpart and promoted virtually complete relaxation of residual stressestherein.

EXAMPLE 4

[0146] A first step of the local forming procedure was carried out in away similar to that of Example 3, whereas a second step was performedusing a built-up forming mandrel and a roll. A forming diagram of adisk, according to the present embodiment, is illustrated in FIG. 18.

EXAMPLE 5

[0147] A first step of the local forming procedure was carried out in away similar to that of Example 3. A second step was effected using aforming mandrel having an outside diameter equal to a minimum insidediameter of the blank peripheral portion.

[0148] As a result of the production process, according to all the threeembodiments, there were manufactured disks having a homogeneousmicrocrystalline structure which satisfies completely, as to shape andsize, the requirements imposed by the drawing.

EXAMPLE 6

[0149] A sleeve-type part was to be obtained from a blank made of theBT25 titanium alloy, having its peripheral portion unilaterally expandedin the direction away from the central portion thereof. A first step ofthe local forming procedure was effected using a single roll and aninternal forming mandrel similarly to Example 3. The thickness of theblank peripheral portion after the first step of the procedure was 12mm. Then the internal mandrel was replaced with an external one, therewas also replaced the roll and there was changed the angle of itsincline relative to the axis of the blank rotation so that local formingof the inner surface of the blank peripheral portion may be performed.

[0150] As a result of the production process according to the presentembodiment, the finished part having well-developed inner and outersurfaces of the peripheral portion thereof was obtained.

EXAMPLE 7

[0151] A part similar to that of Example 6 was to be manufactured. Afirst step of the local forming procedure was effected as in Example 6,but unlike Example 6 a second step of the local forming procedure wascarried out with two rolls which were disposed on the opposite sides ofthe wall being formed of the blank peripheral portion.

EXAMPLE 8

[0152] A sleeve-type part was to be obtained from a blank made of theBT25 titanium alloy with an original coarse-grained structure, saidsleeve-type part having its peripheral portion unilaterally tapered inthe direction away from the central portion thereof.

[0153] Local forming was effected using a preformed blank having acentral and a peripheral portion which is shaped as a unilateralprojection. The blank having an outside diameter of 450 mm and theprojection thickness of 50 mm was prepared by virtue of die-forging,whereby a coarse-grained structure was established therein with aparticle size of 200 to 500 □m. A first step of the local formingprocedure was effected using a forming mandrel and a single roll, bothbeing preheated to 990-960° C. in the working furnace. Local forming ofthe blank peripheral portion into the shape of the type of a cylindricalsleeve having a constant outside diameter was performed in three stepsusing reversal of the roll motion. At the first step the thickness ofthe blank peripheral portion was reduced to 35 mm. At the second andthird steps the deformation temperature was decreased by 10-20° C. Theperiod of the blank rotation relative the roll was 100 s at the firststep, and 25 and 20 s at the second and third steps, respectively. As aresult, the thickness of the blank peripheral portion was reduced to 25and 12 mm, respectively. An analysis into the microstructure of theblank peripheral portion conducted after the third step demonstratedthat a microcrystalline structure with a particle size of 5 to 7 □msimilar to Example 1 was established. Further on, the cylindricalforming mandrels were replaced by the built-up ones that follow theinternal shape of the blank peripheral portion, whereupon the walls ofthe sleeves made at the first step were reduced on the built-up mandrelsunder the same conditions. First the forming mandrel was replaced with abuilt-up one, whereupon final forming of the peripheral portion waseffected as in Example 4. Final operation of local forming was carriedout in two steps, the period of the blank rotation with respect to theroll was 25 s, and at the second step, 5 s. During the first operationthe period of the blank rotation relative to roll was longer than duringthe second operation, which is due to the fact that with acoarse-grained structure of the blank material a more prolonged periodof time is required for stress relaxation than with a fine-grainedstructure thereof. In the latter case the extent of the grain boundariescontributing to activation of the grain-boundary slippage is muchincreased, as well as to efficient stress relaxation in superplasticdeformation.

EXAMPLE 9

[0154] A sleeve-type part was to be obtained from a blank made of theÝÏ962 powder nickel alloy (Ni-13Cr10.1Co-4.3Mo-3.2Al-2.6Ti-3.4Nb-2.8W)and having its peripheral portion unilaterally tapered in the directionaway from the central portion thereof. The shape of the finished partand of the forming blank are the same as in Example 3. Used for localforming was a blank with the microcrystalline structure prepared forsuperplastic deformation, said structure being of the microduplex typewith the particle size of 2-3 □m obtained by the powder metallurgicaltechnique. The blank peripheral portion was preformed into the shape ofthe sleeve type having a wall thickness of 12 mm, ready for final localforming procedure which was effected using a single roll similar to asecond operation in Example 3. The preheating temperature of the blankand mandrel was 1050° C. Use was made of a roll similar to that ofExample 1.

[0155] As a result of the production process according to a givenembodiment, there was made from the hardly deformable ÝÏ962 nickelalloy, practically for one operation of local forming, a part having itsperipheral portion unilaterally tapered in the direction away from thecentral portion thereof.

[0156] As a result, the part produced according to a given embodiment issimilar, as to shape, to that obtained in Example 4.

EXAMPLE 10

[0157] A sleeve-type part was to be obtained from a blank made of anickel alloy (Ni-16Cr-13Co-4Mo-4W-2.1Al-3.7Ti) and having its peripheralportion tapered in the direction away from the central portion thereof.Local forming procedure was carried out using a preformed blank having acentral and a peripheral portion appearing as a unilateral projection.The blank having an outside diameter of 410 mm and a projectionthickness of 25 mm was produced by die-forging technique, whereby a5-micron homogeneous microcrystalline structure of the microduplex typewas established. Used as an original die-forging blank was a cylindricalblank cut out from a hot-pressed rod 230 mm in diameter. Die-forging waseffected in a 1600-ton press under quasi-isothermal conditions. Theblank was preheated to 1050° C., the die, to 950° C.

[0158] The operation of local forming of the blank peripheral portionwas carried out using a forming mandrel and a single roll similarly toExample 3. The preheating temperature of the blank and mandrel in theworking furnace was 1050° C. The roll was heated in the preheatingchamber to a temperature 100 to 200° C. below that indicated above. Theroll was introduced into the working furnace together with its carrier,while the roll-to-carrier attachment unit was subjected to intercoolingwith compressed air admitted to pass through the ducts provided in theroll carrier. As a result of local forming there was made the finishedpart of a preset configuration with the thickness of its peripheralportion equal to 12 mm. An analysis into the microstructure of the blankperipheral portion gave evidence of the fact that just after rotaryextrusion the microstructure of the blank peripheral portion retainedits fine-grained nature with the particle size of ˜5 μm. With a view toeliminating residual internal stresses caused by a change in the diskgeometry, there was carried out annealing of the disk in a diphaseγ+γ′-region under the following conditions: heating the disk to 850° C.followed by holding for an hour, then heating to 950° C. followed byholding for two hours, next temperature rise to 1050° C. followed byholding for 8 hours. Whenever it was necessary to obtain a morecoarse-grained structure homogeneous over the entire cross-section ofthe part, temperature was raised to 1150° C., followed by holding fortwo hours and cooling down to room temperature. As a result of such aheat-treatment procedure, a homogeneous structure with the particle sizeof 20-30 μm was established in the disk peripheral portion. Thus, whenusing a cooled tool carrying out additional specified annealing in adiphase γ+γ′-region rules out any possibility of developing grain sizevariations in the part peripheral portion.

[0159] While preferred embodiments of the invention have been described,the present invention is capable of variation and modification andtherefore should not be limited to the precise details of the Examples.The invention includes changes and alterations that fall within thepurview of the following claims.

What is claimed is:
 1. A method for making an intricately-shapedaxisymmetric part having a central portion and a peripheral portion,comprising: simultaneously rotating a blank structure fixed on a shaftand forming a peripheral portion of the blank using a forming toolhaving at least three degrees of freedom (i) at a temperature above 0.4the blank melting point but below the temperature of secondaryrecrystallization, (ii) at a rate of from 10⁻³ to 10² s⁻¹, and (iii) fora rotation period to effect stress relief in the portion being formed.2. The method of claim 1, wherein at least a part of the peripheralblank portion has an outside diameter exceeding the diameter of afinished part or an inside diameter less than the diameter of a finishedpart.
 3. The method of claim 1, wherein the blank structure has not beenpreconditioned for superplastic deformation.
 4. The method of claim 1,comprising preconditioning the blank structure for superplasticdeformation.
 5. The method of claim 1, wherein forming the blankcomprises reducing the blank structure peripheral portion by rolling ina direction toward its central portion.
 6. The method of claim 1,comprising forming an aluminum blank structure for a period not inexcess of 0.25 s.
 7. The method of claim 1, comprising forming atitanium blank structure or heat resistant nickel alloy blank structurefor a period of 0.25 to 100 s.
 8. The method of claim 1, comprisingforming a coarse-grained blank structure for a period of 0.5 to 100 s.9. The method of claim 1, comprising forming a fine-grained blankstructure for a period of 10 to 50 s.
 10. The method of claim 1,comprising forming a submicrocrystalline blank structure for a period of0.25 to 10 s.
 11. The method of claim 1, comprising forming the blankstructure in a number of steps determined by the preformed condition andmaterial of the blank structure.
 12. The method of claim 1, comprisingpreparing the blank structure for superplastic deformation andpreforming the blank structure into the shape of a sleeve, whereinforming the peripheral portion is completed in a single step.
 13. Themethod of claim 1, comprising preparing both a central portion and theperipheral portion of the blank structure for superplastic deformationand forming a sleeve-shaped blank in a first step and forming the shapedpart from the blank in a further step.
 14. The method of claim 1,comprising performing a coarse-grained blank structure into a centralportion and a thin-walled peripheral projection and forming thepreformed blank into a sleeve-shaped blank being prepared in a firststep and subjecting the sleeve-shaped blank to 50-75% reduction undersuperplaticity temperature and deformation rate conditions.
 15. Themethod of claim 1, comprising forming in a first step effected byreversal roll motion.
 16. The method of claim 1, comprising using aforming mandrel to form a part having varying thickness and diameterdimensions.
 17. The method of claim 1, comprising forming in a firststep effected by reversal roll motion and using a forming mandrel toform an interior surface of the blank structure.
 18. The method of claim1, comprising forming in a first step effected by reversal roll motionand using a forming mandrel to form an exterior surface of the blankstructure.
 19. The method of claim 1, comprising forming in a first stepeffected by reversal roll motion and using a built-up forming mandrel ina further forming step.
 20. The method of claim 1, comprising forming ina first step effected by reversal roll motion and using a formingmandrel heated within a superplasticity range of the blank structure ina further forming step.
 21. The method of claim 1, comprising preparingthe blank structure for superplastic deformation and preforming theblank structure into the shape of a sleeve having a monotonicallynarrowing shape, wherein forming the peripheral portion is completed ina single step.
 22. The method of claim 1, comprising preparing the blankstructure for superplastic deformation and forming the blank structureinto the shape of a sleeve having a monotonically narrowing shape,wherein forming the peripheral portion utilizes a single roll and aforming mandrel having an outside diameter equal to a minimum insidediameter of the blank peripheral portion.
 23. The method of claim 1,wherein forming comprises using a first roll to form on a first side ofthe blank structure in a first step and using the first roll and asecond roll at an opposite side in a second step.
 24. The method ofclaim 1, comprising forming a fine-grained heat-resistant nickel alloyblank stricture at a temperature from the deformation temperature to atemperature of superplascity of the structure.
 25. A device for makingintricately-shaped axisymmetric part having a central portion and aperipheral portion, comprising an axial blank structure fixing androtating unit including a fixture for interchangeably installing amandrel including a built-up mandrel; at least one roll with a carrier;actuating mechanism for rotating and displacing the roll relative to ablank structure fixed by the unit; a furnace for heating the blankstructure fixed by the unit, the furnace having a movable portiondisposed around a window for introducing the roll into the furnace;wherein the movable portion of the furnace is axially movable togetherwith the roll over an entire working stroke length of the roll.
 26. Thedevice of claim 25, wherein the blank structure fixing and rotating unitcomprises a shaft and sleeve for imparting torque to the blankstructure.
 27. The device of claim 25, wherein the roll carrier furthercomprises a heat shield.
 28. The device of claim 25, comprising tworolls disposed on the opposite sides of a wall of the blank structure.30. A method for making a part having a central portion and a peripheralportion, comprising: preconditioning a blank structure for superplasticdeformation; forming the blank structure into the shape of a sleevehaving a monotonically narrowing shape in a first step, forming acomplete peripheral portion of the sleeve in a single second step (i) ata temperature above 0.4 the blank melting point but below thetemperature of secondary recrystallization, (ii) at a rate of from 10⁻³to 10² s⁻¹, and (iii) for a rotation period to effect stress relief inthe portion being formed.
 31. The method of claim 30, comprising using aroll and a mandrel to form the sleeve shape in the first step andforming the complete peripheral portion in the single second step by useof two rolls disposed on opposite sides of a forming wall of theperipheral portion.